472 FORMATION OF LYMPH 



leaves the blood and enters the lymph, although it ought not to do so 

 by diffusion, while water, which might pass from the hypotonic blood 

 into the lymph by osmosis, moves in the same direction from the blood 

 to which the isotonic salt solution has been added. Regulative mechan- 

 isms, in short, exist which tend, with, but also without, the co-opera- 

 tion of diffusion and osmosis, and even, so to say, in their teeth, 

 to bring back the quantitative and qualitative composition of the 

 blood to the normal. Exactly similar phenomena are witnessed when 

 the equilibrium is upset from the other side by the injection of salt 

 solutions into the subcutaneous tissue or the intramuscular connective 

 tissue. Hypotonic sodium chloride solution injected into the sub- 

 conjunctival connective tissue quickly loses water and gains sodium 

 chloride, as it ought to do if under the influence of osmosis and diffusion, 

 and hypertonic salt solutions gain water. But eventually hypertonic, 

 hypotonic, and isotonic solutions, and even serum itself, are completely 

 absorbed, which could not occur in the presence of diffusion and 

 osmosis alone. Sometimes in dropsy it appears that the oedema liquid 

 is absorbed when the patient is put on a diet free as far as possible 

 from salts. The suggestion is that the regulative mechanism which 

 tends to keep the molecular concentration of the blood and lymph 

 approximately constant provides that as the salt content of the body 

 falls, which it does through continued excretion of salts in the urine, 

 water is eliminated in corresponding amount. 



The Contribution of the Tissue-Cells to the Lymph. So far we 

 have considered the passage of the lymph constituents, on the one 

 hand through the endothelium of the blood capillaries into the 

 tissue spaces ; on the other, from the tissue spaces through the endo- 

 thelium of the lymph capillaries. But it is not to be supposed that 

 the liquid lying in clefts, partly bounded by blood capillaries, partly 

 by lymph capillaries, partly by tissue-cells, should be affected solely 

 by the first two. The third anatomical element must contribute 

 something to, or withdraw something from, the tissue liquid, and 

 may thus play a part in the formation of lymph from the latter. 

 The recent researches of Asher and his pupils have raised the ques- 

 tion of the relation between the physiological activity of the organs, 

 and especially of the glands, and the formation of the lymph. They 

 conclude that the common doctrine that lymph is simply a diluted 

 blood-plasma is erroneous. Lymph*, they say, far from being a 

 mere nitrate or even a secretion from the blood, is formed by the 

 activity of the organs, and may actually be absorbed by the blood 

 from the tissue spaces. In fact, according to their view, the in- 

 travenous injection of lymphagogues, both crystalloid and colloid, 

 only causes an increased flow of lymph in so far as it leads to in- 

 creased glandular secretion. But this generalization has had only 

 a short-lived vogue, and one by one some of the main results which 

 seemed to support it have been disproved or shown to be capable 

 of interpretation in a different sense. For example, it was stated 

 that secretin causes a flow of lymph from the lymphatics of the 

 pancreas, as well as a flow of pancreatic juice. But it has been 

 shown that the increased production of lymph is not due to the 



